\documentclass[12pt]{article}   
 \textheight15cm \textwidth11cm \parindent0mm \parskip 1ex plus2ex minus0.8ex
\begin{document}
Rule boxes may be visible, as for example the following boxes:
\rule{3em}{2ex} \rule[-2ex]{5pt}{3ex}. \\@@rm {}
Rule boxes may be invisible as well, just like this one
immediately following the comma,\rule[-3ex]{0pt}{5ex}.
Here an invisible box modifies the (vertical) depth of the line;
thus it has an effect in spite of being invisible.
This is made plain by the following rule box
\fbox{\rule{0pt}{4ex}\rule{3em}{0pt}} here.\\@@rm {}
By means of \verb|\raisebox| you may raise (or lower) a box
\raisebox{-1ex}[1ex][0ex]{Box}.
This lowering or raising has no effect to the inter-line gap,
as in the previous example.
 
Here is \fbox{a box} in the middle of a line\linebreak
Here is \framebox[40mm]{a box} in the middle of a line\linebreak
Here is \framebox[40mm]{a\hfill box} in the middle of a line\linebreak
Here is \framebox[40mm][l]{a box} in the middle of a line\linebreak
The current
\fbox{\parbox{15mm}{\sloppy a small text in box 1}}
\fbox{\parbox[t]{15mm}{\sloppy a small text in box 2}}
\fbox{\parbox[b]{15mm}{\sloppy a small text in box 3}}
line

\parbox{60mm}{
The following text will have line breaks in paragraph mode. \par
Of course you might use the {\tt minipage} environment instead.
Within a {\tt minipage} environment you can even use footnotes etc.
}
\end{document}